1. Field of the Invention
The present invention relates to a piezoelectric substance element, a liquid discharge head utilizing the same and an optical element.
2. Description of the Related Art
Research is being made in forming ferroelectric or dielectric materials into a thin film and utilizing it in a piezoelectric substance element such as MEMS or an optical element. Particularly research is being actively made in forming a film of perovskite type oxides of ABO3 type and utilizing it as a device such as a piezoelectric substance element or an optical element, and attempts are being made in controlling the crystal orientation of the perovskite type oxide thereby, improving the characteristics of the device.
For example Japanese Patent Application Laid-Open No. H06-350154 discloses a thin film of lead zirconate titanate (PZT) having a rhombohedral <111> orientation of 70% or higher within a compositional range normally assuming a tetragonal structure, and a thin film of the same material having a tetragonal <001> orientation of 70% or higher within a compositional range normally assuming a rhombohedral structure.
Also Japanese Patent Application Laid-open No. 8-186182 discloses a PZT film showing a compositional change in the thickness direction of the film.
However, in the films of the former, the crystal phase in a bulk state of composition and the crystal phase in a thin film are inverted, presumably because a state having a film stress in a thin film is retained. Also because of this inversion in the crystal phases, desired satisfactory characteristics may not be obtained in case of forming a thin film. Also the latter film is a film of tetragonal only with a gradient in the composition, and desired piezoelectric characteristics may not be obtained.
Also a method of obtaining a film of satisfactory characteristics with a PZT film in MPB region is disclosed in U.S. Pat. No. 7,042,141(B2). It describes a PZT (111) film in which a tetragonal and a rhombohedral are present in mixture. Also FIG. 2 of this patent reference exhibits a view indicating mixed crystal phases. Also FIG. 8 indicates, in a mixed-phase region of the PZT (111) film, that Zr/(Zr+Ti) ratio is from 0.40 to 0.65. However, there is no description on the film of satisfactory characteristics in the PZT {100} film. Therefore, this patent reference is considered not to include description on a mode of {100} film in which crystal phases of satisfactory characteristics are present in mixture.